1. Field of the Invention
The present invention is related to a hub unit with a rotating speed sensor which is used to rotatably support an automobile wheel with a suspension apparatus, while it is used to detect the rotation speed (rpm) of the wheel.
2. Description of the Related Art
A hub unit with rotation speed (rpm) sensor that is used to rotatably support an automobile wheel with respect to a suspension apparatus, and that is used to control an anti-lock brake system (ABS) or traction-control system (TCS) by detecting the rotation speed (rpm) of the wheel, has been disclosed in U.S. Pat. No. 4,907,445 as shown in FIG. 1.
The hub unit with rpm sensor shown in FIG. 1 comprises a hub 3 that has a flange section 1 located on its axially outer end (left end in FIG. 1) to secure the automobile wheel (not shown) and a first inner raceway 2a located around the outside peripheral surface in the center of the hub 3, an inner ring member 4 that is fitted around the outside peripheral surface in the center of this hub 3 and has a second inner raceway 2b around its outside peripheral surface, a nut 6 that is screwed onto a male screw portion 16 formed on the outside peripheral surface of the axially inner end (the right end in FIG. 1) of the hub 3 so as to press against the axially inner end face of the inner ring member 4 and to secure this inner ring member 4 to a prescribed location on the outside peripheral surface of the hub 3, an outer ring member 9 that has outer raceways 8a, 8b in rows around its inside peripheral surface and a mount section 7 around its outside peripheral surface for securing it to the suspension apparatus (not shown in the figures), and a plurality of rolling bodies or members 10 that are located between the hub 3 and the outer ring member 9. Thus, the hub 3, to which the automobile wheel (not shown) is secured, is rotatably supported inside the outer ring member 9 that is supported by the suspension apparatus.
In FIG. 1, there is a cylindrical tone wheel 29 securely fitted around the axially inner half (right half in FIG. 1) of the inner ring member 4. An uneven section 12 is formed on the axially inner end face of the tone wheel 29 (this is the end surface facing inward in a widthwise direction when installed in the vehicle; the right end face in FIG. 1) and the magnetic characteristics of this end face change, alternating at equal intervals around the tone wheel 29 in the circumferential direction. Moreover, a cover 34 covers the opening on the axially inner end of the outer ring member 9. Provided in this cover 13 is a sensor 35 whose axially outer end face is opposed to the uneven section 12 of the tone wheel 29.
When using the hub unit with rpm detector constructed as described above in FIG. 1, the automobile wheel (not shown) secured to the flange section 1 formed on the axially outer end of the hub 3 is supported so that it rotates freely with respect to the suspension apparatus (not shown) to which the outer ring member 9 is supported. Also, as the tone wheel 29 secured around the inner ring member 4 rotates as the automobile wheel rotates, the output of the sensor 35, which is faced to the uneven section 12 formed on the axially inner end of the tone wheel 29, changes. The frequency at which the output of the sensor 35 changes is proportional to the rotational speed (rpm) of the automobile wheel, and therefore if the output signal from the sensor 35 is input into a controller (not shown), the rotation speed (rpm) of the wheel can be used to adequately control an ABS or TCS.
The prior art hub unit with rpm detector as described above has problems that must be solved.
Specifically, it is difficult to make it compact in size, therefore the type of vehicle that it can be installed in is limited to comparatively large-sized automobiles. In other words, because the sensor 35 to detect the rotation speed (rpm) of the automobile wheel is axially faced to the uneven surface 12 formed on the axially inner end face of the tone wheel 29, large dimensions in the axial direction of the rpm detection section could not be avoided.
Especially in the case of a relatively inexpensive device, simple magnetic material (not permanent magnetic material) is used for the tone wheel 29, and a so-called passive type sensor having a coil wound around a magnetic core is used as the sensor 35 facing this tone wheel 29. In the case of this passive sensor 35, in order to maintain the output of the sensor 35, the dimensions of the sensor 35 in the axial direction become somewhat large. As a result, the axial dimension of the hub unit with rpm detector is increased in the axial direction.
Besides the hub unit with rpm detector described above, the structures disclosed in Japanese Patent First Publication KOKAI No. H1-175502 and in Japanese Utility Model First Publication KOKAI No. H3-99676 have also been known.
In the construction described in No. H3-99676 and No. H1-175502 mentioned above, the magnetic characteristics of the inside or outside peripheral surface of the tone wheel changes in the circumferential direction, and the detection section of the sensor is faced to the inside or outside peripheral surface of the tone wheel. However, in the case of the construction described in these publications, the core material of the passive type sensor is placed in the axial direction, and so it is desirable to make it more compact.
Furthermore, in Japanese Utility Model First Publication KOKAI No. H4-36121, the tone wheel, which rotates together with the outer ring member, is constructed so that its inside peripheral surface is faced to the sensor. However, in this case, the construction to which the tone wheel is applied differs from the construction in the present invention, and the conditions of its use are limited.
In European Patent Publication No. 0426298A1, a structure is disclosed where the tone wheel secured to the end portion of the hub is rotatable with the automobile wheel and its outer peripheral surface is faced to the inner peripheral surface of the annular sensor which is supported by the cover fittingly fixed to the outer ring member.
In this structure, the inner ring member is fitted onto the hub, and the tone wheel and a stop ring to prevent the inner ring member from being removed from there are provided in series in the axial direction of the hub. Since the sensor is of an annular shape, the sensor output can be increased. On the other hand, the installation space for the tone wheel must be large, so that compacting is difficult.
In order to reduce the dimensions of the hub unit in the axial direction, so that it is possible to install the hub unit in compact-sized automobiles having limited installation space, and thus simplifying the design of the vehicle, the hub unit with rpm sensor as shown in FIGS. 2 and 3, is disclosed in the copending Japanese patent application under No. H5-48365, which is hereinafter referred to as the previous invention. A hub 3 is formed with a flange section 1 on the outside peripheral surface of the axially outer end (this is the end that faces outward when installed in the vehicle; the left end in FIG. 2) of the hub 3 for securing the automobile wheel (not shown). There is a first inner raceway 2a and stepped section 15 formed around the outside peripheral surface in the middle portion of the hub 3.
Furthermore, an inner ring member 4 having a second inner raceway 2b formed around its outside peripheral surface, is fitted, for supporting, around the outside peripheral surface of the hub 3, and its axially outer end (left end in FIG. 2) comes into contact with the stepped section 15.
Incidentally, in place of forming the first inner raceway 2a directly on the outside peripheral surface of the hub 3, it is possible to form it on another inner ring member (not shown in the figure) that is separate from the hub 3, and this another inner ring member and the inner ring member 4 can both be secured around the outside peripheral surface of the hub 3.
There is a male screw portion 16 formed around the axially inner end portion (the portion located on the inside in the width direction when installed in the vehicle; right side in FIG. 2) of the hub 3. A nut 6 screws on to this male screw portion 16, and by tightening it, the inner ring member 4 is secured in a prescribed place around the outside peripheral surface of the hub 3. A mount section 7 is formed around the outside peripheral surface in the middle portion of an outer ring member 9 that is located around the hub 3, and it is used to secure the outer ring member 9 to the suspension apparatus (not shown).
Moreover, there are outer raceways 8a, 8b formed around the inside peripheral surface of the outer ring member 9 and faced to the first and second inner raceways 2a, 2b, respectively.
Also, there are a plurality of rolling bodies or members 10 located between the first and second inner raceways 2a, 2b and the outer raceways 8a, 8b, and they allow the hub 3 to freely rotate inside the outer ring member 9.
The "inner raceway" and "outer raceway " are also referred to as "inner ring raceway" and "outer ring raceway".
Furthermore, there is a seal ring 17 between the inside peripheral surface on the axially outer end of the outer ring member 9 and the outside peripheral surface of the hub 3, so that it closes off the opening on the axially outer end of the space where the rolling bodies or member 10 are located between the inside peripheral surface of the outer ring member 9 and the outside peripheral surface of the hub 3.
Also, on the axially inner end of the hub 3, there is a cylindrical end section 22 with constant diameter located further axially inward than the male screw section 16, and formed to stick out from the axially inner end of the nut 6, so that a tone wheel 29 is supported by this cylindrical end section 22. The outer diameter of the cylindrical end section 22 is smaller than the groove or bottom diameter of the male screw 16.
The tone wheel 29 is made of magnetic sheet metal such as steel sheet that is formed by pressing, drawing, or another plastic working. This tone wheel 29 comprises an inner cylindrical section 19 with a smaller diameter, an outer cylindrical section 20 with a larger diameter that is concentric with the inner cylindrical section 19, and an annular section 21 that connects the two cylindrical sections 19 and 20. The tone wheel 29 is generally circular and has a cross-section that is crank-shaped.
There are a plurality of through-holes 33 that penetrate the outer cylindrical section 20, and by evenly spacing these through-holes 33 in the circumferential direction, the magnetic characteristics of the outside peripheral surface of the outer cylindrical section 20 are changed, alternatively at equal intervals in the circumferential direction.
The inner cylindrical section 19 of this tone wheel 29 is fitted around and secured to the cylindrical end section 22 formed on the axially inner end of the hub 3. With the tone wheel 29 secured to the hub 3 in this manner, the outer cylindrical section 20 is located around the nut 6.
Also, by closing off the opening on the axially inner end of the outer ring member 9 with a cover 34, it is possible to prevent dust or water from getting inside the outer ring member 9 through the opening. This cover 34 is made of sheet metal such as stainless steel and is formed by a processing method such as drawing.
The axially outer end (left end if FIGS. 1 and 2) of this cover 34 has an opening. Provided on the outside peripheral surface of the axially outer end near the opening of the cover 34 is a protruding support section 25 that is flange shaped. The outer diameter of the axially outer end of the cover 34 in a free state is the same or a little larger than the inner diameter of the opening in the axially inner end face of the outer ring member 9. As a result, the axially outer end of the cover 34 near the opening is fitted into the opening on the axially inner end of the outer ring member 9, so that the protruding support section 25 comes into contact with the axially inner end face of the outer ring member 9.
Moreover, a passive-type sensor 35 is fastened and secured at a prescribed location inside this cover 34. The output signal of this sensor 35 is fetched from the lead wires (not shown in the figure) connected to the connector 26 located on the outside surface of the cover 34. The detection section 27 of the sensor 35 is faced inward in the radial direction of the cover 34. With the cover 34 securely fitted into the axially inner end of the outer ring member 9, this detection section 27 is faced to the outside peripheral surface of the outer cylindrical section 20, and is separated by a small gap or clearance 28 of 0.6 to 1.0 mm.
Furthermore, the core material of the sensor 35 is arranged so that it runs in the circumferential direction of the tone wheel 29 (front to back in FIGS. 2 and 3). At least one end of this core material is bent inward in the radial direction to form the detection section 27, and it is very close to and faced to the outside peripheral surface of the tone wheel 29.
The hub unit with rpm sensor of this previous invention, constructed as described above, supports the automobile wheel so that it rotates freely with respect to the suspension apparatus, and its function in detecting the rotation speed (rpm) of the automobile wheel attached to the flange section 1 of the hub 3 is substantially the same as the prior art hub units with rpm sensor previously mentioned.
In the hub unit with rpm sensor of this previous invention, the sensor 35 of the passive type having a larger axial length is located on the radially outside of the tone wheel 29, and elongated in the circumferential direction, so that the dimensions of the hub unit with rpm sensor are reduced in both the axial and radial directions, making it possible to be installed a limited space in compact-sized automobiles etc.
The hub unit with rpm sensor constructed as described in the previous invention reduces its size in the axial direction, making it possible to install in compact automobiles etc. with limited installation space, and simplifying the vehicle design, when compared to the prior art constructions. But, it is still desired that the following points be improved.
In other words, it is desired that the output of the sensor 35 is raised (the change in output voltage is made larger) in order that the rotation speed (rpm) of the automobile wheel fastened to the hub 3 can be detected correctly. On the other hand, in order to amplify the output of the passive sensor 35 due to the change in voltage that accompanies the change in density of the magnetic flux that passes through the yoke or stator, the size of the sensor 35 must be increased, or the density of the magnetic flux of the permanent magnet (magnetic force) installed in the sensor must be increased.
The space that the sensor 35 can be installed in is limited, therefore the amount that the size of the sensor 35 can be increased is also limited. In addition, the amount that the density of the magnetic flux of the permanent magnet can be increased is also limited, and even if a permanent magnet with a high magnetic flux density is installed in the sensor 35, whose yoke or pole piece has only a small cross-section, the magnetic flux becomes easily saturated in the yoke or pole piece. If the magnetic flux becomes saturated, the output of the sensor 35 is reduced.
In the structure as disclosed in European Patent publication No. 0426298A1, since the sensor is of an annular shape, the saturation in magnetic flux leading to the output reduction hardly occurs. On the other hard, since the axial dimension is inclined to be larger, there are problems in practical use of the hub unit with rpm sensor in the compact cars in which the installation space is limited.